The present invention relates to a filtration system for cleaning impurities from a liquid bath used for the purpose of cleaning or washing metal parts prior to the surfaces of the metal parts being provided with a protective and/or decorative coating.
In order to properly apply protective and/or decorative coatings to metal parts, it is usually necessary to first clean the surfaces of the part which are to receive the coating. This is frequently done by immersing the part in a liquid bath. The liquid in the bath is typically a solvent or solution which is formulated to remove contaminants from the surface of the metal parts. The contaminants washed from the surface of the metal parts accumulate in the bath liquid. In order to continue cleaning or washing the metal parts it is necessary to keep the concentration of the contaminants in the bath liquid below a maximum acceptable concentration. Above that maximum acceptable concentration, an undesirable amount of contaminants would remain on the metal parts when they are removed from the liquid bath. One way by which the concentration of the contaminants in the bath liquid are kept below the maximum concentration is by replacing the bath liquid with clean liquid when the maximum concentration is about to be reached. The removed bath liquid may be hauled away, or it may be treated off-line to remove the contaminants, and thereafter either sewered or if for environmental reasons properly disposed of, or reused.
Alternatively, a filtering system may be provided which cycles the cleaning liquid through an on-line filter to remove contaminants from the liquid bath, thereby maintain the maximum concentration of contaminants in the bath below the maximum permissible concentration. Such a filtering system may operate without regard to whether or not the bath is in use for cleaning metal parts. Further, such a filtering system may be controlled to begin operation when the concentration of contaminants in the bath reaches a predetermined level, and to stop operating when a certain minimum concentration of contaminants is reached. This invention relates to an improvement in the latter type of filtering system.
In accordance with this invention, a filtering system is provided which cycles the cleaning liquid in a liquid bath through an on-line filter to remove contaminants from the cleaning liquid. A processing tank is connected for cleaning liquid flow to and from a liquid bath tank. A flow path is provided from near the bottom of the bath tank, to near the bottom of the processing tank. A porous filter element is submersed in the bath tank. A flow path through the porous filter is provided to and from the processing tank. A pump drawing cleaning liquid from the processing tank causes it to pass through the flow path in the porous filter, and back to the processing tank. While liquid is being pumped through the flow path in the porous filter, the pressure on the liquid is greater than the fluid pressure in the liquid bath tank surrounding the porous filter. Thus, cleaning liquid passes through the pores of the porous filter from the flow path to the liquid bath. The pores in the filter are sized to prevent contaminant from passing there through. Thus, cleaned liquid is returned to the liquid bath tank, and cleaning liquid with an increased concentration of contaminants is returned to the processing tank. When the concentration of contaminants in the processing tank reaches a predetermined level, the contaminated cleaning liquid must either be disposed of, or filtered to remove the contaminants and stored or returned to the filtering system for further use.
The present invention will be understood by reference to the following drawings and description.